The reason I think it's harder in the short run to choose celebration over blame is that you have to take responsibility for more of your own bad outcomes, you have to be grateful for what you have when you're plainly receiving less than someone else, and you have to make a conscious decision to assess individuals and discrete situations solely on their merits, instead of just lumping them all into some category of Things You Already Know. In other words, you have to assign yourself to the role of student in life, instead of the more secure feeling Master of All Knowledge.
Choosing optimism is choosing vulnerability and humility on an ongoing basis, and that's often in conflict with our nature.
Great quote from Washington Post columnist Carolyn Hax on how easy it can be to remain unhappy. Please read the rest via Kerry's blog.